Timoor Sakharuk

Effects of Finite Switching Frequency and Delay on PWM Controlled Systems

December 14, 1998
3:00 PM
422 Snell

Abstract

The thesis examines the effects of (low) switching frequency and delays on systems with pulse-width modulated (PWM) power supplies. Open- and closed- loop modeling procedures are described together with analytical formulas. Deviations from standard (idealized) models which replace a PWM power supply unit with a fixed gain are quantified. In DC drives low switching frequency reduces the effective PWM gain, and delays make the gain larger than the idealized one at low voltages. The necessary and sufficient condition for existence of a T-periodic stable equilibrium in the closed-loop linear system with a DC PWM is obtained. This result is based on an analysis of a piecewise affine discrete-time map under an assumption of linear-ripple approximation. Experimental results are provided for a PWM controlled DC servo motor, while analytical results are presented for some standard DC/DC examples from the power electronics literature. Thesis also presents analysis of the PWM supplied AC drives under space vector modulation. The magnitude of the current ripple in the closed-loop system is estimated, open- and closed-loop PWM gain is evaluated.

Thesis Committee:
Prof. Aleksandar M. Stankovic (advisor)
Prof. Gilead Tadmor
Prof. Brad Lehman